Acoustic amplifier



May 20, 1930. H. E. HALL 1,759,614

ACOUSTIC AMPLIFIER Original Filed April 21. 1924 J? RFLEC rave awn-0c:

wau/vn shape of a torus,

Patented May 20, 1930 UNITED STATES PATENT OFFICE HARRY E. HALL, or sr. CHARLES, ILLINOIS, ASSIGNOR T0 FREEMAN- AND SWEET, or CHICAGO, ILLINOIS, A COPARTNERSHIP COMPOSED or HADLEY r. FREEMAN AND DONALD H. SWEET ACOUSTIC AMPLIFIER Application filed April 21, 1924, Serial No. 707,825. Renewed September 20, 1929.

My invention relates to delivering large volumes of sound from a source having sufiicient energy for such delivery, but being itself of insufiicient magnitude to act on sufficient volumes of air. While I have illustrated the invention as applied to a horn or a loud speaker unit for radio work, it will be obvious that the principles of the invention are applicable in a large number of other instances.

In the accompanying drawing, the figure is a central vertical section of a loud speaker unit and horn according to the principles of the invention.

In the embodiment of the invention selected for illustration, the loud speaker unit 10 is threaded directly into the central aperture of the base casting 12, which casting is continued outwardly to define trough 14, annular lip 16 and an outer annular flange 18 provided with three rubber feet'20. In the particular assembly shown, the holding ring has been removed from the loud speaker unit, and the casing is threaded directly into part 12, which has a flange 22 to hold the diaphragm in place. A suitable aperture is provided at 24 for passage of the electriccord 26.

The walls of the horn shown, define what may be termed a continuously enlargingpassage comprising a plurality of reversely extending annular passes connected at their ends by chambers, each chamber having the truncated substantially adjacent its equator. Tube 28 for the first pass fits. tightly at the bottom in the base casting. The next tube on the base casting is 30. This flares upwardly, but its contact surface at 32 with the supporting base is a true cylinder, so that it canbe assembled by merely slipping itin place.

Three oppositely extending tubes 34, 36 and 38 together with the top walls joining them, constitute a one-piece unitary headtelescoped with the base and the tubes carried thereby. The path of the sound emanating from the loud speaker unit is from oral cavity 40 through central resonator tube 28, chamber 42, down inside dispersion tube 34, through chamber 44, up inside base tube 30, through chamber 46,- down inside amplitube 36,

through chamber 48, up inside reflecting tube 16, through chamber 50, and down inside emission tube 38 which last tube terminates in a flared lip 52. The curved outer surface of the base at 53, being a continuation of the inner wall of the emission tube, cooperates in delivering the sound to the surrounding air. The small end of tube 28 is approximately half the diameter and one quarter of the area of the effective vibrating surface of the diaphragm of the loud speaker unit 10. Taking the area of the small end of tube 28 as a unity, the area at the large end is approximately 1.8. The actual areas in one successful embodiment are 0.6013 and 1.1075 square inches, with a tube length of 5% inches.

Chamber 42 is the smallest torus and thus defines a central tip or dispersion cone 54. In entering this chamber the pulsation is spread out into an annular form. The area of the passageway as it leaves chamber 42 is greater than where it enters the chamber by another increment substantially equal to the increment in area in passing through tube 28. It will be noted that the distance from the edge of tube 28 to cone 54 is greater than the distance outwardly to wall 34, but the outer annulus is of greater diameter than the inner, so that the progressive increment in area in passing through chamber 42 is as stated.

( In the next pass inside tube 34, the areais again enlarged by another increment of the same amount or value. In obtaining this result, it is necessary to take into account the inclination of the walls of tube 28. In the embodiment shown, I make these two increments equal, by making tube 34 substantially a true cylinder. In passing through chamber 44 another increment of area is added, and tube 30 is flared outwardly to define, with tube 34, the next pass providing another increment of area. Chamber 46 provides another increment, and tube 36, being a true cylinder, duplicates the increment between tubes 34 and 30. Chamber 48 provides the eighth increment, and tube 16 the ninth. Beginning with the tube 16 the increase. in area is no longer in equal increments, this tube, cham-' ber 50 and tube 38 flaring to increase the area at a more rapid rate. The areas of each passage have been designed so as to permit vibratory motion without any noticeable cushion effect and yet not great enough in area to cause a loss of vibratory inertia. All the tubes are of different lengths to prevent the occurring of a natural period.

In each of chambers 44 and 4.6 I prefer to provide three or more coil springs 56 held in place by integral lugs or pins 58, on which they fit snugly, and at the mouth of the horn I provide a plurality of springs 60 stretched across the annular opening. These have the eflect of damping out any vibrations or oscillations tending to originate in the horn itself, as distinguished from the pulsations delivered by the loud speaker. I

The material I prefer to employ is aluminum, but it will be obvious that considerable variations in acoustic properties of the finished article may be obtained by the use of various materials. The aluminum wall provides a comparatively hard and unyielding surface for reflection and guiding of the sound.

In manufacturing and assembling the article, the head is built up in stages, by casting cylinders 34 and 36 down to dotted lines 62 and 64 separately, and then casting all the rest .of'the head in a mold containing cylinders 34 and article in one piece. Lip 16 is similarly .united at 65 to the supporting base. Tube 28 is simply slipped into place and its lower edge hammered over a trifle. Tube 30 is slipped into place and held in position by the tension ofsprings 56 only. Tubes 36 and 16 are each provided with a plurality of rivets 66 cast integrally thereon, preferably three for each tube, and the opposing chambers 48 and 50 are drilled with registering apertures. Final assembly merely involves telescoping the two halves, and riveting over the heads of rivets 66.

Without further elaboration, the foregoing will so fully explain the gist of my invention,-

that others may. by applying current knowL edge, readily adapt the same for use under various conditions of service, without eliminating certain features which may properly be said to constitute the essential items of novelty involved, which items are intended to be defined and secured to me by the following claims.

I claim:

, 1.. In an acoustic amplifier, in combination,

a base, a loud speaker unit supported thereby, oral cavity over the said base defining an diaphragm of said un1t, and walls defining an annularly convoluted enlarging passage opening downwardly above the outer edge of said base.

2. In an acoustic amplifier, in combination, a base, a loud speaker unit supported thereby,

' said base defining an oral cavity over the 36 to produce the finished diaphragm of said unit, and walls defining an annularly convoluted passage opening downwardly above the outer edge 'of said base.

3. An fining an annular wall extending axially of the the outer wall, the extending portion inner wall flaring out radially.

4. An acoustic amplifier having a diaphragm, an oral cavity in phragm, and walls defining a passageway leading out of said cavity, said passageway being of increasing cross-section throughout its entire length, and having a first portion, an annular return portion extending back outside said first portion, and another annular portion encircling both said first mentioned portions, all said portions being defined by surfaces of revolution capable of generation by movement of a straight line.

5. An acoustic amplifier having a diaphragm, an oral cavity in front of said diaphragm, and walls defining a passageway leading out of said cavity, said passageway being of increasing cross-section throughout its entire length, and having a first portion, an annular return portion extending back outside said first. portion, and another annular portion encircling both said first mentioned portions, all said portions being defined by surfaces of revolution'capable of generation bymovement of a straight line,

acoustic amplifier having walls deexit for sound, the inner annulus beyond of said said portions being connected by half toruses .in which the area of the passage is also increased.

6. An acoustic amplifier having walls defining an annular exit for sound, the inner wall of said exit extending axially of the annulus beyond the outer wall, said inner wall beyond the plane of the outer wall having no material inward change of slope for an axial distance of the same order of magnitude as the radial dimension of said exit.

7 An acoustic amplifier having a diaphragm, an oral cavity in front of said diaphragm, and walls defining a passage way leading out of said cavity, said passageway having a first portion of substantially uniform taper, and an annular return portion of substantially uniform taper extending into the end of said first portion opposite said cavity to define a chamber in the form of a half torus connecting said portions.

8. An acoustic amplifier, comprising a pair of sound directing me bers arranged in spaced concentric relationship to form a tortuous passage, each of said members being constructed of a plurality of truncated members connected together to form continuous curved surfaces, sage is free fromv sharp edges and corners, said sound directing members being of such shape that the tortuous passage is of gradfront of said dia whereby the tortuous pasually increasing cross-sectional area throughout its length. p

9. An acoustic amplifier having a diaphragm, an oral cavity in front of said diaphragm, and walls defining a passageway leading out of said cavity, being of increasing cross-section throughout its entire length, and having a first portion, an annular return portion extending back outside said firsfportion, and another annular portion encircling both said first mentioned portions, the first two of said portions being defined by surfaces of revolution capable of generation by movement of a straight line, said portions being connected by half toruses in which the area of the passage is also increased.

In Witness whereof, I hereunto subscribe my name this 17th day of April, 1924.

' HARRY E. HALL.

said passageway 

